A rotary cutting tool is a hand-held power tool having an electric motor that rotates a cutting tool bit at high speeds. Such tools are particularly useful for cutting sheets of material such as drywall and plywood. The cutting tool bit includes a sharp cutting edge that is wrapped in a helix around the axis of the bit. The cutting tool bit is designed for cutting perpendicularly to the axis of the bit. The electric motor that drives the bit is enclosed in a motor housing. The motor housing is generally cylindrical in shape, with the cutting tool bit extending from one end of the motor housing along the axis of the housing. The cutting tool is used to remove material from a workpiece by moving the rotating cutting tool bit through the workpiece in a direction perpendicular to the axis of the rotation of the bit. It is conventionally operated by grasping the motor housing with one or both hands, turning on the electric motor to begin high speed rotation of the cutting tool bit, spinning the cutting bit into a workpiece, such as a piece of wood, and then moving the cutting bit through the workpiece in a direction perpendicular to the axis of the cutting tool bit by moving the motor housing in a direction parallel to the plane of the workpiece surface while keeping the axis of the motor housing generally perpendicular to the workpiece surface.
The utility of a rotary cutting tool may be enhanced by attaching accessories to the cutting tool. For example, although a rotary cutting tool allows a user to form cuts in a workpiece perpendicular to the axis of an attached cutting tool bit, the cuts that are made are generally freehand cuts. Forming a perfect circular cut or aperture in a workpiece may prove difficult without some additional means for ensuring that all points on the cut are equidistant from a center point of the circle. One method commonly used for forming a circle or circular aperture in a workpiece involves drawing a circle with a compass and following the line with the rotary cutting tool. A difficulty with this method is that the rotary cutting tool may slip from the drawn circle.
What is desired, therefore, is an attachment for a rotary cutting tool or other hand-held power tool that allows a user of the power tool to form circles or circular apertures in a workpiece. There is also a need for an attachment that allows the formation of circles or circular apertures having a variety of sizes. There is a further need for an attachment that allows the formation of circles or circular apertures having a smaller diameter than that of the power tool. There is yet a further need for an attachment that includes a measurement scale for determining the size of the circle or circular aperture to be formed by the power tool prior to the formation of the circle or circular aperture. There is even yet a further need for an attachment that allows a user to form circles or circular apertures in a workpiece and also allows the user to set the depth of a cut to be made by the power tool.
It would be desirable to provide an apparatus and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed herein extend to those embodiments which fall within the spirit and scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.